Technical Field
The present disclosure relates generally to the field of combustion furnaces and methods of use to produce glass, and more specifically to methods and systems to control bubble size and/or foam decay rate in glass handling equipment downstream of a submerged combustion melter.
Background Art
A submerged combustion melter (SCM) may be employed to melt glass batch materials to produce molten glass by passing oxygen, oxygen-enriched mixtures, or air along with a liquid or gaseous fuel, or particulate fuel in the glass batch, directly into a molten pool of glass usually through burners submerged in a glass melt pool. The introduction of high flow rates of products of combustion of the oxidant and fuel into the molten glass, and the expansion of the gases cause rapid melting of the glass batch and much turbulence, and possibly foaming.
While traditional, non-submerged combustion melters may to a lesser degree suffer from the problems discussed herein (and therefore may benefit from one or more aspects of this disclosure), molten glass produced by an SCM is typically about 30 percent void fraction or more with small bubbles that may have a range of sizes distributed throughout the molten mass of glass. These are referred to herein as “entrained bubbles.” This void fraction is much higher than molten glass produced by traditional, non-submerged combustion melters. For good glass fiber production from an SCM or other melter, it is preferred that the bubbles be allowed to coalesce and rise to the surface giving good, clean, well-defined molten glass in lower regions of downstream channels and forehearths to be delivered to a forming operation, such as for continuous e-glass fibers. With regard to SCMs, attempts to reduce the foam through SCM process adjustments, such as use of helium and steam to scavenge and consolidate bubbles, sonic methods to consolidate bubbles, vacuum to increase bubble size, and centrifugal force have not met with complete success in reducing foam from an SCM to an acceptable amount. Certain SCMs and/or flow channels may employ one or more high momentum burners, for example, to impinge on portions of a foam layer. Such methods and burners are disclosed in Applicant's U.S. Pat. No. 9,021,838. Various methods and systems for de-stabilizing the foam layer in equipment downstream of an SCM are proposed in Applicant's U.S. patent application Ser. No. 13/644,058, now U.S. Pat. No. 9,492,831 issued Nov. 15, 2016 (use of low-momentum burners or lancing H2, O2, N2, Ar, and/or air) and in Applicant's U.S. Pat. No. 9,096,452, (vibrate forehearth, impact foam with acoustic waves, impact foam with solids, and/or impact foam with a mechanical apparatus, with or without vibration). On the other hand, for production of foam glass products from an SCM, it may be preferred to maintain the bubbles in their entrained state.
Despite the above efforts, it would be an advance in the glass manufacturing art if foam production in an SCM could be controlled other than by destroying some of the foam after it has formed during melting of glass-forming materials.